The present invention relates to percussion machines and, more particularly, to electromagnetic percussion hammers and related devices.
Percussion machines of various designs and sizes are used in a wide range of application, including, but not limited to, construction, mining and various industrial and medical applications.
A typical percussion machine includes a hollow housing through which a piston is reciprocated. The piston periodically impacts an instrument, such as a suitable chisel-like member, which extends beyond the housing. To operate a percussion machine, the distal tip of the instrument is brought into contact with the work piece to be impacted and the percussion machine is activated, causing the piston to reciprocate within the housing and to impact the instrument which transits the shock to the work piece.
Various methods for causing the piston to reciprocate within the housing are available. These include various pneumatic systems which use air pressure to cause the reciprocation of the piston within the housing. A disadvantage of pneumatic percussion hammers is that they must include, or be directly connected to, a source of high pressure air, typically a compressor with its attendant motor. This renders the unit bulky and difficult to transport and thus less versatile in many applications where it is desired to move the unit frequently.
To overcome the above-referenced disadvantage, it has been proposed to drive the piston electromagnetically. In a typical electromagnetic percussion hammer a portion of the housing includes an electromagnet and the piston includes a permanent magnet. The direction of current through the electromagnet is cycled at the desired rate in order to reciprocate the piston. The permanent magnet is attached in some suitable manner to the piston body, which must be made of a non-magnetic material, which greatly limits the materials which can be used and which often forces the use of a material which is less than optimal from the point of view of strength and durability. Typically, the permanent magnet is in the form of a ring which is fixedly embedded in the piston body. A disadvantage of fixedly connecting the permanent magnet to the piston body is that the repeated shocks during operation tend to loosen the connection between the permanent magnet and the piston body and lead to early failure of the device. Furthermore, the non-magnetic portion of the piston needs to be made of two or more parts to allow for assembly and disassembly of the unit which further weakens the unit and reduces its life and reliability.
In an attempt to overcome this difficulty, it has been proposed to mount an annular permanent magnet within an external slot in the piston body in such a way that the magnet is able to travel axially within a confined region defined by an anterior and a posterior portion of the piston body. In such a system arrangements are made to ensure that the two bodies are not in contact with each other at the moment the piston body impacts the instrument. In this way, the impact of the piston body on the instrument is not directly transmitted to the permanent magnet. A difficulty with such a solution is that to assemble a piston unit wherein the piston body forms a confined region through which the annular permanent magnet can travel requires that the piston body be made of at least two portions. This non-monolithic construction is undesirable since the piston body is, as a result, susceptible to failure upon repeated impacts.
There is thus a widely recognized need for, and it would be highly advantageous to have, a highly reliable and durable electromagnetic percussion hammer whose piston body can be made of a single monolithic block of a suitable material.